JP3203566B2 - Wide-angle lens - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a wide-angle lens for photography, and more particularly to a wide-angle lens suitable for an inexpensive camera for panoramic photography and a film unit with a lens.

[0002]

2. Description of the Related Art In recent years, a lens-equipped film unit has been widely used as an inexpensive camera that can be easily used. A wide variety of cameras are commercially available. Of which, normal 3
There is a camera that covers the top and bottom of the shooting screen size of 5mm film with a mask, etc., and obtains a panoramic picture by enlarging and printing it as a horizontally long screen. This type of camera takes advantage of the features of panorama A wide-angle lens is desired.

As a wide-angle lens usable for such a purpose, there are a lens having a stop between two positive meniscus lenses disclosed in US Pat. No. 4,932,764 and US Pat. -16
JP-A-3-259108 discloses a lens system having a negative meniscus lens disclosed in Japanese Patent No. 3509 and a positive meniscus lens disposed behind the negative meniscus lens and having a diaphragm disposed behind these lens units. A lens comprising a single lens having a positive meniscus and a diaphragm disposed behind the single lens is known.

However, of these lenses, US Pat. No. 4,932,764 and US Pat.
In the lens disclosed in No. 2, the lenses are arranged on both sides of the stop, and the light beam passing through the lens behind the stop passes through a wide range, and when the shutter is arranged behind the lens system, a large aperture is required. Shutter speed is required, and it is difficult to obtain a sufficient shutter speed. Therefore, if a shutter is provided between the two lenses, the structure of the lens system and the shutter function becomes complicated, and it is difficult to provide an inexpensive camera.
In the wide-angle lens disclosed in JP-A-3-163509, since a negative lens having a strong refractive power is located in front, the back focus of the lens and the overall length of the lens become too long, which undesirably leads to an increase in the size of the camera. Japanese Patent Laid-Open No. 3-259108
In the single lens disclosed in the publication, the chromatic aberration of magnification increases as the angle of view increases, and the image quality of a panoramic print enlarged from a normal print becomes insufficient.

[0005]

SUMMARY OF THE INVENTION An object of the present invention is to obtain a wide-angle lens which is compact and has a sufficient image quality even in an enlarged print for panorama.

[0006]

As shown in FIG. 1, the wide-angle lens according to the present invention has a meniscus first lens having a convex surface facing the object side and a concave surface facing the object side in order from the object side. It consists of a positive meniscus second lens,
When the focal length of the first lens is f ₁ , the focal length of the entire system is f, the radius of curvature of the object side surface of the second lens is r ₃ , and the axial thickness is d ₃ , the following conditions are satisfied. I do. −0.1 <f / f ₁ <0.4 (1) 0.08 <d ₃ / | r ₃ | <0.25 (2)

It is desirable to satisfy the following conditions secondarily. However, when a slight reduction in performance is allowed, such as when the printing magnification is small or the angle of view is reduced, it is indispensable. It is not a condition. If the radius of curvature of the first lens on the object side is r ₁ , the axial thickness is d ₁ , and the axial distance between the first lens and the second lens is d ₂ , the following conditions are satisfied. _{0.15 <r 1 /f<0.25 (3)} 0.03 <d 1 /f<0.07 (4) 0.03 <d 2 /f<0.08 (5)

[0008] More preferably, at least one surface of the first lens and the second lens is aspherical, and the aspherical surface of the first lens is such that the positive refractive power becomes weaker from the center to the peripheral portion, or it is negative. And the aspherical surface of the second lens is shaped such that the positive refractive power becomes stronger from the center toward the periphery. More specifically, when the object side surface of the first lens is an aspheric surface, the curvature decreases as going from the center to the peripheral portion, and the image side surface of the second lens is an aspheric surface. Is an aspherical surface whose curvature increases from the center toward the periphery.

In the wide-angle lens according to the present invention, the stop is set to the second position.
It is arranged near the lens, that is, immediately after the second lens or immediately before the second lens.

[0010]

The wide-angle lens according to the present invention has a meniscus shape.
The two lenses are arranged so that the concave surfaces face each other, and the structure is close to symmetry, and it is easy to correct coma and astigmatism.
Further reduce the positive refractive power of the first lens, or
By giving a slight negative refracting power and making the second lens have most of the refracting power of the entire system, it is possible to prevent the occurrence of chromatic aberration of magnification. Conditional expression (1) relates to the arrangement of the refractive power. If the lower limit of the conditional expression (1) is exceeded, the negative distortion becomes large, and the back focus and the overall length of the lens become long, so that a compact lens cannot be obtained. If the upper limit is exceeded, lateral chromatic aberration and positive distortion will increase.

Further, the chromatic aberration of magnification can be favorably corrected by making the object side surface of the second lens concave so as to have a diverging function and giving an appropriate axial thickness. Conditional expression (2) relates to the shape of the second lens. When the value goes below the lower limit, sufficient correction of lateral chromatic aberration cannot be performed, and the curvature of field becomes too large. Beyond the upper limit, negative distortion increases,
Astigmatism also increases.

If the lower limit of conditional expression (3) is not reached, decentering of the image plane due to the eccentricity of the first lens and the second lens is liable to occur. Not a suitable lens. When the value exceeds the upper limit, the radius of curvature of the image side surface of the first lens becomes large, and the coma aberration at a low angle of view involving the paraxial radius of curvature becomes large, which is not preferable. If the lower limit of conditional expression (4) is exceeded, the field curvature becomes too large or the axial thickness of the lens becomes too thin, which causes problems in workability and strength. If the upper limit is exceeded, chromatic aberration of magnification increases. If the lower limit of conditional expression (5) is exceeded, the field curvature will increase. In addition, the height at which the concave surfaces of the first lens and the second lens collide with each other is reduced, so that the F-number of the lens becomes darker or the peripheral light quantity tends to be insufficient. Beyond the upper limit, negative distortion becomes large.

Further, an aspherical surface is provided on the first lens such that the positive refractive power becomes weaker or the negative refractive power becomes stronger from the center to the peripheral portion, and the center portion is provided on the second lens. By arranging an aspheric surface whose positive refracting power becomes stronger as it goes toward the periphery, the flare of the peripheral rays of the off-axis light beam is corrected, and when the imaging surface is curved, an appropriate curvature of field is obtained. Can be given. In view of these effects, it is preferable that the aspherical surface is disposed apart, and desirably, it is disposed on the object side surface of the first lens and the image side surface of the second lens.

[0014]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the wide-angle lens according to the present invention will be described below. The symbols in the table represent the following. r: radius of curvature of the refractive surface d: interval between the refractive surfaces nd: refractive index of the lens material νd: Abbe number of the lens material F: F number ω: half angle of view The aspherical surface of the present invention is represented by *, and its shape is When the direction of the optical axis is the X axis and the direction perpendicular to the optical axis is the Y axis, it is expressed by Equation 1.

(Equation 1) Here, r is a paraxial radius of curvature, and K and A ₂ i are aspherical coefficients. Further, in the following embodiment, the imaging surface has a radius of curvature R = 1.
Reference numeral 10 denotes a cylindrical surface that curves toward the lens in the longitudinal direction of the screen.

First Embodiment f = 25.4 F = 9.7 ω = 41 ° Surface No. rd nd νd * 1 4.582 1.000 1.492 57.0 2 4.595 1.00000 3 −20.408 3.000 1.492 57.0 * 4 −8.720 Aspherical surface coefficient First surface K = −0.1917 A ₄ = −0.426 × 10 ⁻³ A ₆ = 0.6340 × 10 ^-Four A ₈ = −0.1238 × 10 ⁻⁴ A ₁₀ = 0.1065 × 10 ⁻⁶ Fourth surface K = 0.1496 × 10 ⁻² A ₄ = −0.7685 × 10 ⁻³ A ₆ = 0.1008 × 10 ⁻³ A ₈ = −0.3329 × 10 ⁻⁴ _{f / f 1 = 0.20 d 3} / | r 3 | = 0.15 r 1 / f = 0.18 d 1 / f = 0.04 d 2 / f = 0.04

Second Embodiment f = 25.4 F = 9.7 ω = 41 ° Surface No. rd nd νd * 1 4.570 1.000 1.492 57.0 2 4.438 1.200 3 -18.528 2.000 1.492 57.0 * 4 -7.904 Aspheric surface first surface K = -0.2472 A ₄ = -0.5208 x 10 ^-4 A ₆ = 0.7025 x 10 ^-Four A ₈ = −0.1892 × 10 ⁻⁴ A ₁₀ = 0.3834 × 10 ⁻⁶ Fourth surface K = 0.1548 × 10 ⁻² A ₄ = −0.7474 × 10 ⁻³ A ₆ = −0.4999 × 10 ⁻⁴ A ₈ = −0.4398 × 10 ⁻⁶ _{f / f 1 = 0.12 d 3} / | r 3 | = 0.11 r 1 / f = 0.18 d 1 / f = 0.04 d 2 / f = 0.05

Third Embodiment f = 25.9 F = 9.7 ω = 40 ° Surface No. rd nd νd * 1 4.970 1.100 1.492 57.0 2 5.098 1.000 3 −17.855 2.000 1.492 57.0 * 4 −8.503 Aspheric surface first surface K = −0.5044 A ₄ = −0.4060 × 10 ⁻³ A ₆ = 0.1268 × 10 ^-3 A ₈ = −0.2543 × 10 ⁻⁴ A ₁₀ = 0.1132 × 10 ⁻⁵ Fourth surface K = −0.6662 × 10 ⁻³ A ₄ = −0.1198 × 10 ⁻² A ₆ = 0.4170 × 10 ⁻³ A ₈ = −0.1199 × 10 ⁻³ _{f / f 1 = 0.25 d 3} / | r 3 | = 0.11 r 1 / f = 0.19 d 1 / f = 0.04 d 2 / f = 0.04

Fourth Embodiment f = 25.4 F = 9.7 ω = 41 ° Surface No. rd nd νd * 1 4.970 1.100 1.492 57.0 2 4.817 1.00000 3. −16.440 2.000 1.492 57.0 * 4 −7.447 Aspheric surface first surface K = −0.4115 A ₄ = −0.6722 × 10 ⁻³ A ₆ = 0.1021 × 10 ^-3 A ₈ = −0.2753 × 10 ⁻⁴ A ₁₀ = 0.1111 × 10 ⁻⁵ Fourth surface K = -0.1195 × 10 ^-2 A ₄ = 0.1337 × 10 ⁻² A ₆ = 0.3773 × 10 ⁻³ A ₈ = −0.1191 × 10 ⁻³ f / f ₁ = 0.09 d ₃ / | r ₃ | = 0.12 r ₁ /f=0.20 d ₁ /f=0.04 d ₂ /f=0.04

[0019]

The wide-angle lens according to the present invention has good imaging performance with little chromatic aberration of magnification and small astigmatism as shown in the examples and the aberration curves, and has a sufficient image quality even in enlarged prints such as panoramas. Is obtained. Further, as seen from the cross-sectional view, the shutter is compact and the shutter can be arranged behind the lens, so that the shape of the lens and the shutter mechanism can be simplified.

[Brief description of the drawings]

FIG. 1 is a sectional view and a ray path of a wide-angle lens according to the present invention.

FIG. 2 is an aberration diagram of a first embodiment of the wide-angle lens according to the present invention.

FIG. 3 is an aberration diagram of a second embodiment of the wide-angle lens according to the present invention.

FIG. 4 is an aberration diagram of a third embodiment of the wide-angle lens according to the present invention.

FIG. 5 is an aberration diagram of a wide-angle lens according to a fourth embodiment of the present invention.

──────────────────────────────────────────────────続 き Continued on the front page (58) Fields surveyed (Int. Cl. ⁷ , DB name) G02B 9/00-17/08 G02B 21/02-21/04 G02B 25/00-25/04

Claims (1)

(57) [Claims] 1. A convex surface is directed to the object side in order from the object side.
In a wide-angle lens composed of a meniscus-shaped first lens and a meniscus-shaped positive second lens having a concave surface facing the object side, the focal length of the first lens is f ₁ , the focal length of the entire system is f, and the second lens is f. A wide-angle lens satisfying the following condition when the radius of curvature of the lens on the object side is r ₃ and its on-axis thickness is d ₃ −0.1 <f / f ₁ <0.4 0.0. 08 <d ₃ / | r ₃ | <0.25